644 PISCES. 



pressed by means of muscles inserted into their bases. Advancing one 

 step further, we find in Silurus the first ray of the pectoral fins enor- 

 mously developed and forming a strong serrated weapon of a very 

 formidable description, which although both in shape and structure 

 exactly comparable to the spine upon the tail of the Fireflare, is never- 

 theless connected by a most beautiful and perfect joint with the bones 

 of the shoulder, so that it might easily be regarded as forming part 

 of the endoskeleton, did not its peculiar structure indicate its real 

 nature. 



(1755.) We thus arrive at the important conclusion that different 

 portions of the exoskeleton become approximated in character to those 

 of the endoskeleton, or, in truth, really convertible into true bone ; and 

 with this fact before us it becomes easy to understand the nature of 

 various parts of the skeleton of a fish, which, upon any other supposi- 

 tion, would be not a little puzzling to the comparative osteologist. 



(1756.) The nature of the rays of the dorsal and anal fin of the Perch, 

 for example, together with the interspinous bones upon which they are 

 sustained, is quite unintelligible if they are regarded as belonging to 

 the endosJceleton ; and no dismemberments of the osseous system as yet 

 imagined, or supposed subdivisions of the vertebra into a greater num- 

 ber of elemental pieces than we have enumerated, has been able to solve 

 the difficulty ; but if they are regarded as ossified derivations from the 

 exoskeleton, all difficulties at once vanish. 



(1757.) Again, the opercular bones (fig. 312, 28, 30, 32, 33) forming 

 the gill-covers of an osseous fish have been a fruitful source of discussion; 

 and M. Geoffroy St.-Hilaire* was reduced to the necessity of recog- 

 nizing in these broad plates the ossicles of the human ear, which, after 

 dwindling to a rudiment in the descending scale of vertebrate animals, 

 suddenly reappeared in a new and exaggerated form. " J'ai peu vu 

 dans la serie des etres de ces resurrections d'organes se remontrant 

 subitement dans une classe apres avoir disparu dans une ou deux de 

 celles qui la precede dans 1'echelle," are the impressive words of Cuvier 

 upon a similar occasion ; and it is certainly far more simple to imagine 

 the epidermic plates of the Sturgeon ossified and converted into bone, 

 than to be compelled to have recourse to the bold speculations of the 

 French anatomist regarding the real nature of these opercular portions 

 of a fish's skeleton f. 



* Philosophie Anatomique des Pieces osseuses des Organes respiratoires. 8vo. 

 Paris, 1818. 



f The different opinions on the nature or homology of the opercular bones may be 

 reduced to two principles : first, that they are modifications of parts of the ordinary 

 skeleton ; secondly, that they are superadded bones peculiar to Fishes : the latter view 

 is that taken by Cuvier. According to the former, which is the more philosophical 

 mode of considering them, three opinions have been offered. The first by Spix and 

 Geoffroy, that they are gigantic representatives of the ossicles of the ear, otherwise 

 absent in the skeleton of Fishes : this view has been adopted by Professor Grant. 



